Sensor devices that detect physical displacement are for example used in a vehicle air bag system for detecting an impact applied to a vehicle at a time of collision. Air bags of the air bag system are triggered based on detection signals produced from the sensor devices, thereby protecting passengers. This kind of collision detecting sensor device is for example disclosed in Japanese Patent Publication No. 2004-294419 (US 2004/0201464 A1).
In the above publication, the sensor device includes a G sensor that produces a signal in response to acceleration due to the collision impact. The G sensor includes a detecting portion, a communication portion, a power source circuit and the like. These elements are packaged. The G sensor is housed in a sensor housing portion of a resinous case. In the resinous case, a connector terminal is integrally fixed such that an end of the connector terminal extends into the sensor housing portion. The G sensor is connected to the end of the connector terminal through a metal lead so as to be electrically connected to an external device through the connector terminal.
In a vehicle, such a collision detecting sensor device is generally located at a position affected by heat such as in an engine compartment. If a temperature largely changes, respective elements of the sensor device thermally expand or contract. In particular, the resinous case has a coefficient of linear expansion generally larger than those of other elements. Namely, the size of the case relatively largely changes with temperature. When the size of the case changes, the connector terminal fixed in the case displaces. As a result, a connecting portion between the connector terminal and the lead and a connecting portion between the lead and the G sensor are likely to receive excessive stress, resulting in breaks in these connecting portions.